In this study, we have used whole-blood transcriptomics to investigate, in a large sample of HCV patients, the following: (1) baseline gene expression differences associated with future development of IFN-α-induced depression, before IFN-α administration, and (2) longitudinal changes in gene expression from baseline to treatment week 4 (TW4) and TW24 of IFN-α, separately in those who did and did not develop depression. The gene discussed is IFNA1; the disease is depressive disorder.